Even though The CW included Flockhart as a regular cast member in Supergirl‘s season three press release, TVLine’s Michael Ausiello says it’s unclear if Flockhart will return full time for the new season:

Despite the fact that Flockhart was listed among the series regulars in Supergirl‘s official Season 3 press release, I’m told she will not rejoin the full-time ranks. But if the scheduling can be worked out, you can count on her putting in a handful of guest appearances, as she did in Season 2.”

This happened in season two. Flockhart, who was a regular in season one, became a recurring star on Supergirl when the show moved its production from Los Angeles to Vancouver. It looks like Flockhart has struck the same deal for season three.